diff -u b/core/lib/Drupal/Core/Entity/ContentEntityForm.php b/core/lib/Drupal/Core/Entity/ContentEntityForm.php
--- b/core/lib/Drupal/Core/Entity/ContentEntityForm.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityForm.php
@@ -483,6 +483,13 @@
   /**
    * {@inheritdoc}
    */
+  public function isEntityDeepSerializationRequired() {
+    return $this->entityDeepSerializationRequired;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
   public function __sleep() {
     $this->entity->setDeepSerialization($this->entityDeepSerializationRequired);
     return parent::__sleep();
only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/Entity/ContentEntityFormInterface.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityFormInterface.php
@@ -75,4 +75,12 @@ public function isDefaultFormLangcode(FormStateInterface $form_state);
    */
   public function validateForm(array &$form, FormStateInterface $form_state);
 
+  /**
+   * Returns the current estimation if entity deep serialization is required.
+   *
+   * @return bool
+   *   TRUE if deep serialization is reqired, FALSE otherwise.
+   */
+  public function isEntityDeepSerializationRequired();
+
 }